1. Field of the Invention
The present invention relates to an antiskid control system which controls slippage of wheels occuring at the time of vehicle braking.
2. Related Art
A conventional anti-skid control system calculates a slip ratio with respect to each of wheels from a vehicle body speed and each wheel speed and maintains a slipping state of each of the wheels in a reasonable state to prevent the wheels from locking.
The anti-skid control system has a master cylinder generating a brake fluid pressure in response to an operation of a brake pedal conducted by a driver and a plurality of wheel cylinders for producing a braking torque to each of the wheels using the brake fluid pressure generated by the master cylinder. The anti-skid control system controls a slipping state of each of the wheels by increasing or decreasing a brake fluid pressure of each of the wheel cylinders (hereinafter, referred to as W/C pressure).
In more detail, when the slip ratio of a wheel becomes large and the wheel has a tendency lock, the W/C pressure of the wheel is decreased by discharging the brake fluid within the wheel cylinder assigned to that wheel into a reservoir. When the tendency of the wheel to lock becomes small due to the decrease of the W/C pressure, the W/C pressure thereof is maintained. Also, when the tendency of the wheel to lock disappears, the W/C pressure thereof is increased at predetermined timing.
In the above-mentioned system, since the W/C pressure is increased using brake fluid pressure generated by the master cylinder, when the W/C pressure is to be maintained, the brake fluid pressure generated by the master cylinder is prevented from being transmitted to the wheel cylinder. At this time, however, the movement of the brake pedal is restricted because the brake fluid pressure is not transmitted from the master cylinder to the wheel cylinder. When the restriction of the brake pedal movement lasts for a long time, the driver harbors a feeling such that the brake pedal cannot be depressed, that is, the brake pedal is like a fixed plate (hereinafter, referred to as "fixed plate feeling"). As a result, an operational feeling of the brake pedal deteriorates.